This project involves the study of rechargeable cardiac pcemakers and pacemaker electrode physiology in both animals and man. The pacemakers utilize both modified silver-mercuric oxide and lithium rechargeable cells. Accelerated tests have shown a potential life span of over 50 years. At present, real time tests are in excess of 5 years. In addition, a multiparameter transtelephonic monitoring system incorporated in the pacers is capable of transmitting such diverse information as cell voltage, rate, hermeticity, cell impedance, lead impedance, heart rate, refractory interval, energy output, lead integrity, and R-wave sensing margin. Recently we have also incorporated a means for transmitting the patient's electrocardiogram from the pacer. All of these functions are done noninvasively. Lithium pacers with multiparameter monitoring are now commercially available and are being used in many human patients. Our lead electrophysiologic studies have led to the development of a new lead system to optimize both pacing and sensing. This basic concept has now been incorporated into commercially available leads.